An admittance tunnel is generally defined as a test set-up for measuring the constitutive parameters of dielectric and magneto-dielectric materials in a plane-wave environment. One of its principal uses is to characterize lossy materials for absorption of electromagnetic energy, which may have attenuation constants in the range of 0.1 dB/inch to 40 dB/inch and relative permittivities in the range from 1.01 to 40. Man-made lossy materials manufactured in bulk quantities may possess local inhomogeneities in the materials. However, since in the typical applications large areas of the materials may interact with the incident wave, the properties measured should be representative of the overall average properties of the materials. Therefore, in these applications, microscopic profiling of the material is not desired. Further, destructive testing that requires many individual samples of the material to be machined to precise dimensions to fit inside a waveguide or transmission line set-up is highly undesirable.